Hammer drills are known which have an intermediate member provided with coupling jaws and cam faces and a striking mechanism formed of a striking element which has follower cam faces and which is biased by a resetting force. The striking mechanism is actuatable by means of a clutch component which is disposed on the tool shaft and which is provided with jaws that cooperate with corresonding coupling jaws of the intermediate member. The clutch component is rotated by means of a drive element.
The actuation of the striking mechanism is effected when the hammer drill is placed against the object to be worked and the tool shaft is axially pressed inwardly. As a result, the jaws of the clutch part on the tool shaft engage the counterjaws of the intermediate member. As the intermediate member rotates by virtue of the engaged state of the clutch component, the abruptly terminating cam faces of the intermediate member repeatedly lift the striking element against the force of a striking (compression) spring and then allow the striking element, propelled by the compression spring, to axially impact the tool shaft. Such a device is disclosed in German Laid-Open Patent Application (Offenlegungsschrift) No. 2,203,072.
A driving stage and a striking mechanism structured as outlined above are disadvantageous in that the tool shaft extends through the intermediate member into the interior of the striking element which in this region has the shape of a hollow cylinder. Consequently, the intermediate member must be mounted in a bearing on the tool shaft and thus friction losses occur even when the tool is used merely as a drill, since the tool shaft moves relative to the intermediate member. Furthermore, in the hammer drill drive of the above structure, the coupling part disposed on the tool shaft is, at the same time, a gear, so that the mass of the rotating and/or axially vibrating tool shaft is unnecessarily large for its purpose. Furthermore, the tool shaft which extends relatively far into the interior of the tool has an adverse effect on the structural length of the tool, on the diameter of the striking mechanism and thus on the entire hammer drill.